Can a haircut ruin a Coton's coat?

by Lulu
(USA)

I have a pair of Coton puppies nearly a year old. At about 6 months we realized wearing a harness had made a mess of their hair. They did not get terribly matted but they had areas that were shorter and ragged where the harnesses sat on their backs. It was summer so we got them clipped short to start over.

One of them had and still has thinner silky hair that barely even needs combing, The other is a big puffy marshmallow who was easy to comb before the haircut and even months later remains difficult to brush and comb, and looks ratty. I wonder if her hair will ever recover. It even got a little curly where it had been straight. The other one was already wavy but she has nice soft waves and that remains just fine.
The haircut was not particularly even and I would like that corrected but I hate to have her clipped again if it will just perpetuate the problem. I am tempted to go to another groomer but they are so good I hate to disrupt them for someone else who may have no clue for Coton grooming either.

I have heard some say to never cut a Coton's hair but plenty seem to be fine with puppy cuts. I am at a loss.